傾斜磁異向性在鉑/鈷/鉑異直結構中對自旋軌道矩無場翻轉的影響

Abstract

隨著物聯網(IOT)設備與高性能計算(HPC)的需求增加，使得磁性記憶體逐漸受到重視。由於電流注入的幾何結構差異，相較於現今量產主流的自旋轉移矩記憶體(STT-MRAM)，自旋軌道矩記憶體(SOT-MRAM)擁有更高的開關速度以及耐用性，但是要實際應用於元件中，我們需要提供外加磁場來打破對稱性以實現磁性的確定性的磁性切換。目前有一種無場翻轉方案是透過在濺鍍過程中將重金屬層斜向生長，以傾斜垂直磁異向性(tilted PMA)。我進一步測試了在鉭/鉑/鈷/鉑/鉭(Ta/Pt/Co/Pt/Ta)不同層之間的斜向生長對於無場翻轉的影響，並且發現了組合不同的斜向生長層可以進一步提高無場翻轉比率並降低翻轉的電流。再經由不同角度的磁滯曲線偏移，可以驗證是由傾斜磁垂直異向性導致的。隨後也探討了退火對於斜向生長鉑晶格結構與無場翻轉的影響，發現退火帶來的原子重新排列與混合會破壞傾斜磁異向性的形成，如何在退火後保留傾斜磁異向性甚至透過退火增強會是一個具有發展潛力的課題。

With the increasing demand for Internet of Things (IoT) devices and high-performance computing (HPC), magnetic memory is gaining attention. Due to the differences in the geometry of current injection, Spin Orbit Torque Magnetic Random Access Memory (SOT-MRAM) offers higher switching speeds and durability compared to the mainstream Spin Transfer Torque MRAM (STT-MRAM) currently in mass production. However, for practical application in devices, an external magnetic field is required to break symmetry for deterministic magnetic switching. Currently, a field-free switching scheme involves the oblique growth of the heavy metal layer during sputtering to tilt the perpendicular magnetic anisotropy (tilted PMA). I further tested the effects of oblique growth between different layers of tantalum /platinum /cobalt /platinum /tantalum on field-free switching and found that combining different obliquely grown layers can further improve the field-free switching ratio and reduce the switching current. Shifts in the hysteresis curves at different angles verify that this is caused by the tilted perpendicular magnetic anisotropy. Subsequently, the effects of annealing on the lattice structure of obliquely grown Pt and field-free switching were also investigated. It was found that the atomic rearrangement and mixing caused by annealing disrupt the formation of tilted magnetic anisotropy. How to retain the tilted magnetic anisotropy after annealing, or even enhance it through annealing, will be a promising topic for further development.